In response to the recent demand for fuel efficient tires, rubber compositions incorporating silica have been used in treads and various other tire components. Silica, on the surface of which there are hydrophilic silanol groups, shows lower affinity for the rubber components, particularly natural rubber, polybutadiene rubber, styrene-butadiene rubber, and other rubbers generally used in tires, than carbon black, and thus tends to provide inferior abrasion resistance and mechanical strength (e.g. tensile strength, elongation at break).
Many techniques for solving the above problem have been proposed, such as for example introducing a modifying group reactive with silica into a rubber component, or using a silane coupling agent to increase the interaction between a rubber component and silica. However, common silane coupling agents have only a limited effect on dispersion of silica because, unfortunately, the functional groups in the molecules react with each other and aggregate before the reaction with silica.
Moreover, Patent Literature 1 discloses the use of a highly reactive mercapto silane coupling agent and the combined use of silane coupling agents. Unfortunately, these techniques still have room for improvement in fuel economy or rubber strength. Furthermore, winter tires require grip performance on ice and snow, and the incorporation of a large amount of silica is known to be effective in improving this property. However, this technique has the above-mentioned problems associated with incorporation of silica.